<template>
  <div class="pdf-basic">
    <p class="pdf-basic__tip">
      <a href="http://mozilla.github.io/pdf.js" target="_blank">pdf.js</a>
    </p>
    <div
      class="pdf-basic__canvas"
      v-loading="fileLoading"
      element-loading-spinner="el-icon-loading"
      element-loading-text="文件加载中"
    >
      <canvas v-for="item in totalPage" :key="item" :id="'the-canvas' + item"></canvas>
    </div>
  </div>
</template>

<script>
import pdfjs from 'pdfjs-dist'
import pdfjsWorker from 'pdfjs-dist/build/pdf.worker.entry'
pdfjs.GlobalWorkerOptions.workerSrc = pdfjsWorker

export default {
  name: 'PdfBase',
  data() {
    return {
      fileLoading: false,
      fileUrl: 'http://www.xdocin.com/xdoc?_key=t7t7z6j54vezfdnwptijcmo63i&_func=down&_dir=math.pdf',
      totalPage: 0
    }
  },
  created() {
    this.loadFile()
  },
  methods: {
    // 加载pdf文件
    loadFile() {
      this.fileLoading = true
      const loadingTask = pdfjs.getDocument(this.fileUrl)
      loadingTask.promise
        .then((pdf) => {
          const totalPage = pdf.numPages
          this.totalPage = totalPage
          for (let i = 1; i <= totalPage; i++) {
            this.renderPage(pdf, i)
          }
          this.fileLoading = false
        })
        .catch(() => {
          this.$message.error('文件加载失败！')
          this.fileLoading = false
        })
    },
    // 以canvas的形式渲染
    renderPage(pdfDoc, pageNumber) {
      pdfDoc.getPage(pageNumber).then((page) => {
        const desiredWidth = 800
        const viewport = page.getViewport({ scale: 1 })
        const scale = desiredWidth / viewport.width
        const scaledViewport = page.getViewport({ scale })

        const canvas = document.getElementById('the-canvas' + pageNumber)
        const context = canvas.getContext('2d')
        canvas.height = scaledViewport.height
        canvas.width = scaledViewport.width

        const renderContext = {
          canvasContext: context,
          viewport: scaledViewport
        }
        page.render(renderContext)
      })
    }
  }
}
</script>

<style lang="scss" scoped>
.pdf-basic {
  height: 100%;

  &__tip {
    margin-bottom: 1em;
  }

  &__canvas {
    min-height: 100%;
    width: 800px;
    margin: 0 auto;
  }
}
</style>
